HomeRoast Digest


Topic: Rosto fuse problems (3 msgs / 155 lines)
1) From: Peter Barnes
Hey all,
I've been writing Steve Glovin at Brightway to try and figure out what 
went wrong with my Caffe Rosto fuse, see what it would take to keep it 
from recurring, etc.  His response is the best reason I've seen yet to 
use a variac:
-------------------
Steve Glovin wrote:
The main reason we find the customers are blowing the thermal fuse is, low
voltage causing a strain on the fuse. If you are in an area that produces
110 volts of electricity and you use a power strip or extension cord you
drop to 103-105 volts causing the machine which is degined to UL
standard volts then the fuse will tend to blow. Your best bet is to plug
the unit directly into the outlet and allow for proper cooling between
roasts. I recommend 30 minutes. Please understand we would not be inclined
to use the fuse at all if UL did not require it.
Steve
-------------------
Now I find this logic odd, because I was getting 119-121V from the 
outlet I was using, but obviously the problems are pretty directly 
related in some way to the current coming from the wall.  Just thought 
I'd share this tidbit for those of you struggling through the blown 
thermal fuse. 
cheers
peter
p.s.  Since I will soon be in the market for a variac, and know very 
little about electricity, could someone guide me to the type of specs I 
should be looking for?  I know there's a link somewhere in the archives 
to a $110 version, but I'd like to spend less than that, if possible.
homeroast mailing listhttp://lists.sweetmarias.com/mailman/listinfo/homeroast

2) From: Mike McGinness
Bah, I disagree with Steve almost 100%. I've been Rosto roasting about two
years, quite a few months with variac. Both with single variac feeding
heater & fan and now dual control split input. I ROUTINELY feed 95-100v to
the heater during equalization stage or high ambient temp. I NEVER wait
between roast batches - go directly from cooling cycle - remove & empty
primary chaff collector - dump beans - invert Rosto and brush out secondary
chaff collector - re-load and roast. 12hrs non-stop back to back no long
cooldown sessions more than once. Low voltage doesn't blow fuses, high
voltage would (actually, fuses are current rated). Thermal fuses blow on
temp. Ok, more than once I've used the Rosto to emulate FR roasting - pushed
135v into for a 4min French roast. No problems what so ever.
I picked up a second Rosto about a year ago. Neither have any issues getting
well hammered. I firmly believe they have made a change in the components
used in the Rosto manufacturing to save money. Too weak or low a rated
thermal fuse. Hence the rash of thermal fuses going out I've heard posted. I
can't seem to kill either of my Rostos no matter what I do:) I guess if I
pused 140v into the heater with NO fan it might fry...
MM;-) aka Kona Konnaisseur miKe mcKoffee
Dual Variable Transformer Rosto Roasting
Rocky grindin' - Miss Silvia brewin'

3) From: dewardh
Mike:
I agree.  What blows the thermal (get that, *thermal*) fuse is insufficient 
airflow over the heater.  Like you I have not been able (well, I haven't really 
tried ) to blow one , over a wide range of voltage, in either of my Rostos. 
 While it may be the case that airflow from the fan falls faster than the heat 
output of the heater coil as voltage drops that is not enough to "blow the 
fuse" at any reasonable voltage . . . *unless there is something else 
restricting the airflow*.
Unfortunately there often is "something else" . . . chaff.  The Achilles Heel 
of the Rosto is the too small chaff collector . . . it too easily clogs, 
dramatically reducing overall airflow.  I'd bet that in most cases of blown 
fuses the roast was a high chaff bean.
There is one other likely cause that is to some degree related to low voltage . 
.. . I have several times seen the recommendation of partially blocking the air 
outlet (with tinfoil) to compensate for either low voltage or a low ambient 
temperature.  While this works it is easy to overdo it (and blow the fuse) if 
one is not monitoring the heater (roast air)temperature.  Of course no-one 
seeking warranty coverage is going to admit having done that . . .
IMO it is almost as important to measure (and control for) roast air 
temperature as it is to measure bean temperature . . . measuring voltage to the 
heater is only an indirect indicator, since the actual air temperature will be 
a function of both power input and the (unmeasured) air flow.  You have avoided 
the problem because your constant attention to agitation keeps you attentive to 
airflow.  Knowing roast air temperature becomes almost essential if you want to 
"automate" (and profile) the roast in a "hot air" roaster . . . it is the only 
way to "wash out" airflow from your control algorithm.
Deward


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